just to make it clear: it stretches your rotator cuff and opens the door to all sorts of shoulder issues, including dangerous instability. I learned the hard way...it is an excellent idea though to hang on an almost straight arm with an already engaged shoulder, as this does exactly the opposite: it protects the joint. If you have trouble seeing what i mean, try this two armed exercise first, it gives the feeling of what is an engaged shoulder Vs a relaxed one. as far as progression goes : my fav would be to start with asym hangs on a campus board, using the pinky of your other hand as low as you can.when you are close to mastering the hold, you want to use the other hand to prevent rotation rather than for "lifting" purposes.
Supplemented with some shoulder free weight exercises in the gym I have made massive progress with this:
I feel stronger and more balanced in my shoulders/ posture and my elbow problems have gone away.
you haven't mentioned any of this revelation to johnny brown have you?